/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.spatial.distance;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.spatial.geometry.Point;
import org.apache.lucene.spatial.geohash.GeoHashUtils;

import java.io.IOException;

/**
 * Implementation of {@link LocationDataSetFactory} that supports location information
 * being contained in a single geohashed field.
 *
 * @see org.apache.lucene.spatial.geohash.GeoHashUtils
 */
public class GeoHashLocationDataSetFactory implements LocationDataSetFactory {

  private final String geoHashField;

  /**
   * Creates a new GeoHashLocationDataSetFactory that will read from the field with the given name
   *
   * @param geoHashField Name of the field containing the geohashes
   */
  public GeoHashLocationDataSetFactory(String geoHashField) {
    this.geoHashField = geoHashField;
  }

  /**
   * {@inheritDoc}
   */
  public LocationDataSet buildLocationDataSet(IndexReader indexReader) throws IOException {
    return new GeoHashLocationDataSet(FieldCache.DEFAULT.getStringIndex(indexReader, geoHashField));
  }

  // ================================================= Inner Classes =================================================

  /**
   * Implementation of LocationDataSet which uses a geohash stored in a single index field
   */
  private class GeoHashLocationDataSet implements LocationDataSet {

    private FieldCache.StringIndex index;

    /**
     * Creates a new GeoHashLocationDataSet which uses the values in the given index
     *
     * @param index A StringIndex containing the values of the geohash field taken from the index
     */
    private GeoHashLocationDataSet(FieldCache.StringIndex index) {
      this.index = index;
    }

    /**
     * {@inheritDoc}
     */
    public Point getPoint(int docId) {
      String fieldValue = index.lookup[index.order[docId]];
      double[] coords = GeoHashUtils.decode(fieldValue);
      return new Point(coords[0], coords[1]);
    }
  }
}
